incrediBILL - 8:33 pm on Aug 20, 2010 (gmt 0)

I've used canonical tags without any problem whatsoever but you have to be careful.

Most errors I've seen so far weren't Google's problems but either misuse of the canonical tag itself with a typo in the URL or some redirect problems.

Reminds me of all the people that complain about bad AdSense targeting yet their SEO on the page is a complete mess.